Computers located within a perimeter of a network communicate with computers outside the boundary of the network in part by sending data packets outbound from the network. The data packets contain information, such as textual messages and multimedia, and metadata, such as a destination addresses and port numbers.
Network administrators employ devices such as firewalls built into routers, certain computer operating systems, and other software, to control information in data packets sent and received over a network. For example, suppose the network includes systems storing sensitive credit card data. A firewall on such a network may have rules to stop outgoing data packets that include textual information resembling credit card numbers (i.e., containing 16 consecutive digits), as such textual information is likely to be a credit card number that should not be sent in an outbound packet as part of an email.
Conventional network security systems, such as network sniffers, test such firewall devices by attempting to send information containing sensitive data in an outbound data packet through the firewall and verifying whether the data packet was blocked by firewall. If the data packet was not blocked, the conventional network security system may adjust the rules of the firewall in order to ensure that data packets containing the sensitive data, or similar data, are blocked in subsequent tests.